a) Field of the Invention
The present invention relates to motor control circuits and, more particularly, to such circuits for stopping motors which provide a reduced stopping time.
b) Background of the Prior Art
In a compact disk player or a photo disk device, it is desired to shorten the waiting time as much as possible before the disk can be removed.
For this purpose, a brake circuit is provided in a control circuit for a spindle motor which rotatively drives a disk in order to rapidly stop the rotation of the disk.
For use as such circuit, a logic type control circuit is known which applies energy to a motor so that it is rotated in a direction opposite to that in which the motor is initially rotated to apply a brake, and the start of the reverse rotation of the motor is detected to stop energization to the motor. This is disclosed in Japanese Utility Model Application LaidOpen No. 195392/l982 (See FIG. 3).
The logic control type circuit described in this publication comprises a discrimination circuit (5) for discriminating a rotational direction of a motor by rotational signals (c) and (d), which differ in phase proportional to the rotational speed of the motor based on the outputs of Hall elements H1 and H2, a memory (6) for storing the discrimination signal of the discrimination circuit, a rotational direction instruction circuit (10) for controlling a motor drive circuit (2) so that the motor is reversely rotated at the time of the stop instruction, a comparator circuit (7) for comparing the discrimination signal of the discrimination circuit (5) with the stored signal of the memory circuit, and a stop circuit (11) for opening a power source of the drive circuit (2) in response to the change in output of the comparator circuit when the motor is reversed.
In this circuit, the rotational direction of the motor is discriminated by the discrimination circuit (5) on the basis of the rotational signals (c) and (d) which differ in phase proportional to the rotational speed of the motor as derived from the rotation detector, and the discrimination signal of the discrimination circuit is stored in the memory circuit (6). The drive circuit (2) is capable of rotating the motor in both clockwise and counterclockwise directions, and at the time of the stop instruction, the motor drive circuit (2) is controlled so that the motor is energized in the direction opposite to the initial energizing direction by the rotational direction instruction circuit (10) to apply a brake in order to reverse the motor. The discrimination signal of the discrimination circuit (5) and the storage signal of the memory circuit (6) are compared by the comparator circuit and the power source of the drive circuit is opened by the stop circuit (11) due to the change in output of the comparator circuit (7) when the motor is reversed.
A D flip flop FF1 constitutes a discrimination circuit (5) in which rotational signals, i.e., clocks having outputs of a rotation detector shaped in waveform (c) and (d), which differ in phase proportional to the rotational speed of the motor as derived from Hall elements for detecting the rotation of the motor, are supplied so that the (d) signal is latched by a change in state (rise) of the (c) signal to thereby discriminate the rotational direction of the motor. The rotational direction instruction circuit (10) prepares a rotational direction signal (f) from a stop signal (stop instruction) (a) and a rotational direction instruction signal (b) to supply it to the motor drive circuit 2. The stop circuit (11) prepares an energization signal, stop-start signal (j), from a stop signal (a) and an output signal (e) of the D flip flop FF1 to feed it to the drive circuit 2. The drive circuit 2 controls the rotational direction of the motor to the normal positive rotational direction when the stop signal (a) is off (low level) and the rotational direction instruction (f) is at a high level, and controls the rotational direction of the motor to the rotational direction opposite the normal direction when the stop signal is on (high level) and the rotational direction instruction (f) is at a low level. That is, this drive circuit 2 determines the normal rotational direction (positive rotational direction) in either clockwise or counterclockwise direction to provide a logic arrangement such that only when the stop signal (a) is on, the motor is rotated in the rotational direction opposite to the normal rotational direction whereas when the stop signal (a) is off, the power source is opened. The drive circuit 2 energizes the motor when the stop signal (a) is off and the energized signal (j) is at a low level to drive the motor in the positive rotational direction. When the stop signal (a) is on as shown in FIG. 4, the rotational direction instruction (f) is at a low level so that the motor is reversely rotated by the drive circuit 2. When the motor is actually reversely rotated, the D flip flop FF1 detects its reversal, the output signal thereof assumes a high level and the energized signal (3) assumes a high level so that the energization to the motor is stopped by the drive circuit 21 and the motor naturally decelerates and stops. In this case, the reversal detection time until the D flip flop FF1 detects the reversal after the motor has been actually reversed changes since the start of reversal of the motor is not in synchronism with the rotational signals (c) and (d) from the rotation detector, but it is, at most, one period portion of the rotational signals.
The reversal of the motor upon application of the brake thereto is detected by comparing the discrimination signal of the discrimination circuit (5) with the storage signal of the memory circuit (6) by the comparator circuit (7). Accordingly, the time until the reversal of the motor is detected after the motor starts to reverse is the total of the time until the discrimination circuit detects the reversal of the motor and the time until the comparator circuit (7) detects the reversal of the motor by comparison of the discrimination signal of the discrimination circuit (5) with the storage signal of the memory circuit (6), which is a total time beyond one period of the rotational signal from the rotation detector. Therefore, the reversing time of the motor becomes extended and the stopping of the motor is delayed.
In the past, when a vibration occurs in the entire apparatus including a motor and as a result the rotor of the motor rotates, the motor sometimes continues to run due to the vibration despite a stop instruction having been issued since the time a rotational signal had been provided from the rotation detector.
The present invention overcomes the above-described disadvantages. It is an object of the present invention to provide a stop control circuit for a motor which is simple in structure and in which, in the case where braking is applied to the motor, reversal detection time until the reversal of the motor is detected after the motor begins to reverse can be considerably shortened, and the stopping of the motor can be performed quickly and positively.